These are already present; they show up on the right side of the screen, next to the direction text. I will consider making them more visible, though.

I have. Unfortunately, WaveNet is not available for download. There are many speech synthesis engines out there that sound better than espeak or flite, but they are all either paid engines, web APIs (which do not work offline and have latency in playback), or research projects like WaveNet which are not available for anyone to use.
Edit: Also, WaveNet is quite slow; on a laptop, it takes about 90 minutes to synthesize one second of speech. On a phone, it would probably be about 5 times slower still.